Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $63.90   3.472%   $66.1186   $66.12   $66.10   $66.10  
  Purchase #2 $98.93   8.730%   $107.5666   $107.57   $107.55   $107.60  
  Purchase #3 $46.75   6.794%   $49.9262   $49.93   $49.95   $49.90  
  Purchase #4 $223.28   8.319%   $241.8547   $241.85   $241.85   $241.90  
  Purchase #5 $30.93   11.535%   $34.4978   $34.50   $34.50   $34.50  
  Purchase #6 $175.74   13.827%   $200.0396   $200.04   $200.05   $200.00  
  Purchase #7 $114.70   9.786%   $125.9245   $125.92   $125.90   $125.90  
  7 purchase totals = $754.23       $825.9280   $825.93   $825.90   $825.90